A towboat is “1. Tugboat, 2. a compact shallow-draft boat with a squared bow designed and fitted for pushing tows of barges on inland waterways”, according to Merriam-Webster Online. This propulsion steered towboat is a displacement type hull, the descendent of canal boats; whose hull pivots about a vertical axis; with a specific forebody, aftbody and midbody. The simple equipment used on the inland waterways relies on flat bottoms and wide beams for stability, and not on liquid ballast, as river water abruptly and forcibly expands when it cools to 32° F. Towboat usage in the United States extends beyond the inland waterways to the intracoastal waterways, and portions of the Great Lakes and the open Gulf of Mexico.
Two sizes of towboats are in use, line boats and harbor boats. The former have up to four propellers, the latter are usually twin screwed; but a variety of single screw boats have been built. Steering rudders are fitted aft of each propeller, with two flanking rudders forward on each side of the propeller shaft. Thus a triple screw line boat usually has nine rudders; the rarer quadruple screw may have twelve rudders, but some of these boats have used large steering rudders in between propellers and omitted (or removed) the outboard flanking rudders.
This multitude of rudders and propellers is a steady source of income to those in the drydocking and repair business. The waterways traversed seemingly conspire to bend rudders, which, in turn, can disable a propeller. The bank itself, rock jettys and uprooted trees are all capable of bending rudders and cupping propellers. Although many ideas have been tried to allow removing propellers without dropping the steering rudders, removal of the aft rudders remains the norm to access the propellers.
The triple screw line boats have an option to increase steering control in fast currents where higher speed is undesirable. Increasing the forward thrust of the outboard screws increases the effectiveness of the steering rudders; to counter the thrust increase, the center screw is reversed. Control is everything going down a winding river, to avoid bank suction and grounding, which can break the wires holding the barges together. Then an operator has not only the swift current, but also loose and damaged barges to round up. Even worse is the possibility of taking out a bridge pier. In the last decade, several such horrific collisions have occurred, with losses to transiting vehicles, including one passenger train.
U.S. Pat. No. 154 claims “The connecting of canal boats by rule-joints, for the purpose of adapting them to the curvature of the canal, and of steering them by their action on each other, upon the same principle with that by which a rudder is made to steer an ordinary boat.” This movement is made manually with a geared tiller against a fixed rack. Another large rudder patent, U.S. Pat. No. 1,364,961, has steerable bows as well as steerable sterns, in a twin hull, with the propulsion between the hulls. It claims “1. A vessel comprising a hull-body provided at its ends with symmetrical, horizontally-swinging steering-sections shaped to form continuations of the hull-body and a diagonally-arranged connection between said sections to cause them to swing . . . ”
U.S. Pat. No. 3,937,171 provides twin hulls connected as a parallelogram, thus directing thrust in an arc limited by the hydraulic rams' range within the cross members. It claims “1. A multihull tugboat . . . comprising: two laterally spaced individual hulls; connecting means connecting the hull for relative longitudinal movement . . . shifting means . . . to selectively move the prow of one hull ahead of the other hull; propulsion means on each said hull.”
The prior art has attempted to increase steering control, but the complexity introduced, and in some instances, the need for multi-unit standardization, have not resulted in usage. The complications and costliness apparent in the traditional steering system invite improvement with a more robust towboat that will perform reliably under the sometime adverse conditions found on the inland waterways.